JPH02227244A - Molding insulated material - Google Patents

Abstract

PURPOSE:To manufacture an insulated material varying its bulk density continuously from the high temperature side to the low temperature side and providing the maximum heat conductivity at respective temperatures by making the bulk density of carbon fiber felts forming respective layers almost constant in the respective layers and reducing the bulk density by stages in the direction square to a bonding surface. CONSTITUTION:A plurality of carbon fiber felts 1a, 1b and 1c are bonded by means of, for example, carbides or graphitized substances 2a, 2b. Bonding is carried out by coating or impregnating a section with resin, and then respective felts are pressurized, heated and integrated, and then calcined and carbonized or graphitized. Bulk density rho1, rho2 and rho3 of a plurality of carbon fiber felts 1a, 1b and 1c is made smaller by stages in the direction square to the bonding surface. That is, a material of large bulk density is used on the high temperature side, while a material of small bulk density is used on the low temperature side, and in between the bulk density is arranged in a manner of getting smaller from the high temperature side to the lower temperature side by stages. The material, therefore, demonstrates superior insulation properties in all the temperature fields in the low and high temperature areas. The bulk density is usually 0.01-0.5g/cm<3>.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a molded heat insulating material suitable as a heat insulating material, a cushioning material, etc. during high temperature heat treatment.

[Prior Art and Problems to be Solved by the Invention] In recent years, high-temperature heat treatment using vacuum evaporation furnaces, semiconductor single crystal growth furnaces, ceramic sintering furnaces, C/C composite firing furnaces, and the like has become important. During this high-temperature heat treatment, the heat insulating material is required to have excellent heat resistance, heat insulating properties, mechanical strength, and durability, and to not cause deterioration of physical properties at high temperatures. Therefore, the usefulness of heat insulating materials using carbon fiber as a starting material is increasing.

In view of the above points, carbon fiber felt is impregnated with a carbonizable resin, the impregnated felt is laminated and compressed to form a molded product having a desired thickness and bulk density, and then the molded product is used as a molded heat insulating material. A manufacturing method has been proposed (Tokuko Sho 5)
0-35930).

However, in this method, since a plurality of carbon fiber felts having the same bulk density are laminated, the bulk density of the obtained molded heat insulating material is constant, and the heat insulating efficiency is not sufficient.

The heat insulating properties of a molded heat insulating material made of carbon fiber felt or the like generally depend on the proportion of voids in the heat insulating material, that is, air spaces with low thermal conductivity, and the orientation of the fibers.

On the other hand, bulk density, temperature and thermal conductivity are the seventh
It was found that there is a relationship as shown in the figure.

In other words, in the medium temperature range, the thermal conductivity of a heat insulating material with a large bulk density and that of a heat insulating material with a small bulk density are reversed.

Therefore, the temperature distribution in a conventional heat insulating material having a uniform bulk density becomes a curve as already shown in FIG. 4 when the bulk density is small and when a1 in FIG. 4 is large. Therefore, if you create a heat insulating material whose bulk density changes continuously from the high temperature side to the low temperature side and the thermal conductivity is the lowest at each temperature, the result will be as shown by C in Figure 4. , the heat insulation performance is the best, and the temperature of the outer surface on the low temperature side is lower than in cases a and b in FIG. 4, showing ideal heat insulation performance.

However, it is industrially extremely difficult to produce such a heat insulating material.

An object of the present invention is to use a plurality of heat insulating materials having different bulk densities to produce a heat insulating material having near-ideal performance.

[Structure of the Invention] The present invention was made based on the fact that in order to ensure excellent heat insulation properties regardless of the external ambient temperature, there is an optimum bulk density of the heat insulating material depending on the external ambient temperature. It is something.

That is, in the present invention, a plurality of layers of carbon fiber felt,
A molded heat insulating material bonded with carbide or graphitized material, or bonded with carbide or graphitized material via a graphite sheet, in which the bulk density of the carbon fiber felt forming each layer is approximately constant within each layer. The above problem is solved by a molded heat insulating material whose bulk density decreases stepwise in the direction perpendicular to the joint surface.

The present invention also solves the above problem by using a molded heat insulating material having a graphite sheet on at least one outer surface parallel to the joint surface.

The definitions of terms used in this specification are as follows.

Infusibility refers to pitch-based fibers in the presence of oxygen, for example, 20
This is a process in which a heat-resistant layer is formed on the surface by heating at a temperature of about 0 to 450°C to prevent melting during firing. Flame-retardant treatment involves heating carbon-containing materials such as phenolic resin fibers other than pitch-based fibers in the presence of oxygen at a temperature of, for example, 200 to 450°C to form a heat-resistant layer on the surface to prevent melting during firing. Refers to the process to prevent.

Carbonization refers to firing a carbon-containing substance such as a phenol resin at a temperature of, for example, about 450 to 1500°C. Graphitization refers to converting carbon-containing substances into
It refers to firing treatment at a temperature of approximately 000°C, and it is included in the concept of graphitization even when the crystal structure is not graphitized.

In this specification, carbon fiber refers to carbonized or graphitized fiber.

Examples of the carbon fibers of the carbon fiber felt constituting the molded heat insulating material of the present invention include carbon fibers made from polymer fibers such as polyacrylonitrile, phenol resin, and rayon, petroleum pitch, coal pitch, liquid crystal pitch, etc. Examples include pitch-based carbon fibers, and at least one type thereof is used.

Appropriate fibers such as fiber diameters of 5 to 30,771 can be used for each fiber.

The thickness of the carbon fiber felt is usually about 5 to 200 mm. Further, the number of laminated layers can be used as appropriate depending on the desired thickness of the molded heat insulating material.

A plurality of carbon fiber felts are laminated and integrated with carbide or graphitized material. Therefore, the mechanical strength of the molded heat insulating material is also high. The carbide or graphitized material used as the bonding agent can be obtained, for example, by firing a resin applied to the bonding surface. As the resin, for example, phenol resin,
Furan resin, xylene resin, urea resin, melamine resin,
Examples include thermosetting resins such as guanamine resin, epoxy resin, diallyl phthalate resin, polyurethane, unsaturated polyester, thermosetting acrylic resin, and polyimide.
Used alone or in combination of two or more. Among the above resins, phenolic resins are particularly preferred.

As shown in Figure 3 (A), the molded heat insulating material is made up of multiple layers of carbon fiber felt (LA) (LB) (LC) bonded with carbide or graphitized material (2a) (2b). As shown in Figure 3(B), graphite sheets (3
), even if the graphite sheet (3) and the carbon fiber felt (la) (lb) (lc) are joined by the carbide or graphitized material (2a) (2b) on both sides of the graphite sheet (3). good. Moreover, as shown in FIG. 3(C), multiple layers of carbon fiber felt (la) (lb) (lc
) may be bonded with a carbide or graphitized material (2b) (2b), and a graphite sheet (3) may be bonded with a graphitized material (2a) on at least one outer surface parallel to the bonding surface. .

In addition, the joining may be done by applying resin to the relevant part, pressurizing and heating each felt to integrate it, and then firing it to carbonize or graphitize it, or by applying resin to each carbon fiber felt. It may be a carbide or a graphitized material formed by impregnating each felt, pressing and heating the felts in a wet state to integrate them, and then firing the felts. In the latter case, it is not necessary to actively apply a resin as a bonding agent.

The bulk densities ρ1 and ρ2 of multiple layers of carbon fiber felt (la) (lb) (lc) constituting the molded heat insulating material are
, ρ3 become smaller stepwise in the direction perpendicular to the joint surface. In other words, a material with a high bulk density is used on the high temperature side, a material with a low bulk density is used on the low temperature side, and in between, the bulk density is gradually decreased from the high temperature side to the low temperature side. Arrange and use as shown.

Therefore, the heat insulating material exhibits excellent heat insulating properties in all temperature fields, both low and high temperatures. The bulk density of the plurality of carbon fiber felts can be set appropriately depending on the temperature at which they are used, but the bulk density is usually about 0.01 to 0.5 g/cj, preferably about 0.1 to 0.35 g/aJ. The density varies within a range. Bulk density is 0. If it is less than 1 g/aJ, not only will the heat insulation properties at low temperatures be insufficient, but the strength will also be low. Moreover, if it exceeds 0.5 g/aJ, the heat insulation properties in the high temperature range will not be sufficient. In addition, the molded heat insulating material with the above structure has better heat insulation properties than a heat insulating material with a constant bulk density distribution, so it is economical because the overall thickness can be reduced, and the heat capacity of the molded heat insulating material can also be reduced. can.

The shape of the molded heat insulating material is selected depending on the application, and may be flat, polygonal, cylindrical, or hollow in cross section.

Note that if the bulk density of the multiple layers of carbon fiber felt decreases in stages, it is possible to ensure heat insulation in the high temperature range and the low temperature range. That is, as shown in FIG. 1, carbon fiber felt (la) with a bulk density ρ of 0.18 g/-
The insulation property in the high temperature range is determined by the bulk density ρ of 0.10 g/c.
The carbon fiber felt (1b) of j can ensure heat insulation in the low temperature range. In the molded heat insulating material, as shown by the solid line in FIG. 2, carbon fiber felts having different bulk densities ρ are laminated and integrated so that the thermal conductivity λ is the smallest at the external ambient temperature T. In addition, even if the low bulk density carbon fiber felt shown by the broken line in Figure 2 or the high bulk density carbon fiber felt shown by the dotted line are used alone, the insulation properties in the high and low temperature ranges are sufficient. Not.

The molded heat insulating material having the above structure can be obtained by impregnating a plurality of carbon fiber felts with different bulk densities with a resin that can be carbonized or graphitized, stacking them, heating them under pressure, and then firing them. That is, as shown in FIG. 5, which is a process diagram, a carbon fiber felt A having a large bulk density and a carbon fiber felt B having a small bulk density are used. Carbon fiber felt A with a large bulk density may be obtained by impregnating carbon fiber felt with a resin, compressing it and firing it, but in this case, the porosity of the carbon fiber felt with a large bulk density decreases. do. Therefore, without using impregnating resin,
It is preferable to produce a carbon fiber felt having a large bulk density as follows.

In other words, infusible pitch-based fibers or carbon fibers (hereinafter collectively referred to as carbon fibers unless otherwise specified) and phenolic resin fibers that have been flame-retardantly treated or not flame-retardantly treated (hereinafter phenolic resin fibers) It can be produced by blending and mechanically bonding and compressing the mixture, and then firing it.

Below, a method for producing carbon fiber felt with a large bulk density without impregnating it with resin will be specifically described.

First, carbon fiber and phenol resin fiber are blended. The blending ratio is usually carbon fiber/phenolic resin fiber-5/
95-9515, preferably 10/90-90/10,
More preferably, it is about 25/75 to 75/25% by weight. If the carbon fiber content is less than 5% by weight, when the mixture is mixed with phenolic resin fibers and spun using a spinning card, the uniformity of the blend may vary and the carbon fibers may form a single fiber. Furthermore, if the carbon fiber content exceeds 95% by weight, it is difficult to increase the bulk density. By adjusting the blending ratio within the above range, the bulk density of the carbon fiber felt can be easily controlled. In addition, it is difficult to produce a carbon fiber felt using only carbon fibers because the shear strength is low, so the fibers are likely to be cut during the mechanical bonding and compression process, which increases the entanglement of the fibers and the bulk density.

Next, after a blended web is formed by forming a sheet of blended fibers, the blended web is mechanically bonded and compressed using a needle punch or the like to increase the bulk density of the felt. The blended web is
It can be produced by a conventional method, such as a method using a spinning card. The direction of the blended fibers may be aligned in one direction, or there may be no directionality. The mechanical joining and compressing means may be a stitching method for stitching the blended web together, but a needle punching method is preferable.

In addition, when blended and bonded and compressed, the mechanical strength does not drop significantly even if the thickness is reduced. The degree of compression and bulk density of the felt can be easily controlled by adjusting the density of the joints, the number of times of joining, etc.

Then, by firing the compressed felt, a high-density carbon fiber felt is obtained.

Carbonization and graphitization in the firing process are usually carried out under vacuum or in an inert atmosphere. Note that when infusible pitch-based fibers are used as carbon fibers, the pitch-based fibers are also carbonized or graphitized.

Next, based on FIG. 5, a method for manufacturing the molded heat insulating material having stepwise different bulk densities according to the present invention will be described using the high-density carbon fiber felt obtained by the above method.

A high bulk density carbon fiber felt A and a low bulk density carbon fiber felt B are impregnated with a thermosetting resin such as a phenol resin diluted with a solvent, and are pressed while heating to be integrally molded. After this, by carbonizing or graphitizing, the third
A molded heat insulating material having a bulk density different in the thickness direction as shown in Figure (A) is obtained. In this case, instead of carbon fiber felt, felts with different bulk densities among carbon fiber felts obtained by blending may be used, or high-density carbon fiber felt and low-bulk density carbon fiber felt may be used. One of these layers may be used and a plurality of the other layer may be used, or a plurality of each layer may be combined.

In addition, as the second manufacturing method, there are the following methods. As shown in FIG. 6, after impregnating carbon fiber felt with the resin solution, it is heated and compressed to a desired bulk density to form a molded body with approximately uniform bulk density. obtain. Two or more carbon fiber felts having different bulk densities are laminated from the obtained molded body so that the bulk densities become gradually smaller, and the plurality of felts are integrated by applying pressure while heating again. At this time, a carbon adhesive that can be carbonized or graphitized is applied to the felt surfaces to be joined.

In addition, in order to further improve the heat insulation performance, a graphite sheet coated with a resin that carbonizes or graphitizes when fired is placed on at least one joint surface, laminated and fired, and a graphite sheet as shown in Figure 3 (B) is placed. Molded insulation may also be made. Furthermore, as shown in FIG. 3(C), a graphite sheet may be attached to the surface and then fired.

[Effects of the Invention] As described above, according to the molded heat insulating material of the present invention, multiple layers of carbon fiber felt are bonded and integrated with carbide or graphitide, and the bulk density varies from one end toward the other end. Therefore, by placing high bulk density felt on the high temperature side and low bulk density felt on the low temperature side,
On the high temperature side, you can enjoy the performance of high bulk density felt with low thermal conductivity, and on the low temperature side, you can enjoy the performance of low density felt with low thermal conductivity, demonstrating excellent heat insulation properties.

Furthermore, when the graphite sheet is arranged on the outer surface parallel to the bonding surface, the heat insulation performance is further improved.

[Examples] The present invention will be described in more detail below based on Examples.

Example 1 A carbon fiber felt with a large bulk density was produced as follows. That is, pitch-based carbon fiber (single fiber diameter 13
-1) 50% by weight (manufactured by Donutku Co., Ltd.) and 50% by weight of flame-retardant phenol resin fiber (trade name: Kynor, manufactured by Nippon Kynor Co., Ltd.) were blended. Next, a blended web is formed, and the bulk density is 0.13 g/cj by double punching.
felt was made. Then, it is fired and carbonized at a temperature of 950°C in an inert atmosphere, with a thickness of about 20 wun and a bulk density of 0.
．． A sheet-like carbon fiber felt A having a large bulk density of 15 g/- was produced.

In addition, as a carbon fiber felt with a small bulk density, pitch-based carbon fiber (single fiber diameter 13p1 made by Donatsuku) was used and needle-bunched in the same manner as above, with a thickness of 20M and a bulk density of 0.05g/-. A small sheet-like carbon fiber felt B was produced.

Carbon fiber felt A with high bulk density and carbon fiber felt B with low bulk density are combined with resol type phenolic resin (
30% by weight methanol solution) was impregnated at an impregnation rate of 70% by weight. Next, each of the above carbon fiber felts A,
The phenol resin was cured by laminating B and pressurizing it with a press, raising the temperature to 170° C. over 1 hour, and keeping at the same temperature for 2 hours. Then, the laminated molded body was taken out from the press machine, heated at a rate of 1°C/min in a nitrogen gas atmosphere, and held at a temperature of 1300°C for 3 hours to be sintered and carbonized to a desired thickness of 31 mm. A molded thermal insulation material having a layered structure and having different bulk densities was obtained. When this molded insulation material was sliced in the thickness direction and the bulk density distribution was examined, one carbon fiber felt had a bulk density of 0.22g/
aJ, the other carbon fiber felt has a bulk density of 0.08 g/
It was in the range of −. The molded heat insulating material thus obtained exhibited excellent heat insulating properties when used with the high bulk density side facing the high temperature side.

Example 2 Carbon fiber felt A obtained in the manufacturing process of Example 1,
The temperature of the laminate B was raised in vacuum at a rate of 3°C/min, and the temperature was increased to 20°C.
A molded heat insulating material with a thickness of about 30 M was obtained by holding at 00° C. for 3 hours and graphitizing it.

Then, when the bulk density distribution of the molded heat insulating material was examined in the same manner as in Example 1, one carbon fiber felt had a bulk density of 0.21 g/aJ, and the other carbon fiber felt had a bulk density of 0.08 g/aJ. -It was. The molded heat insulating material thus obtained exhibited excellent heat insulating properties when used with the high bulk density side facing the high temperature side.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional view showing a molded heat insulating material which is an example of the present invention, and Fig. 2 is a relationship between external temperature T, thermal conductivity λ, and bulk density ρ of the heat insulating material in the molded heat insulating material shown in Fig. 1. 3(A), 3(B), and 3(C) are schematic cross-sectional views each showing an example of the laminated state of the molded heat insulating material of the present invention, and FIG. 4 is a schematic diagram showing the temperature distribution of the molded heat insulating material. , FIG. 5 is a process diagram showing an example of the method for manufacturing a molded heat insulating material of the present invention, FIG. 6 is a process chart showing another example of the method for manufacturing a molded heat insulating material of the present invention, and FIG. 7 is a process diagram showing an example of the method for manufacturing a molded heat insulating material of the present invention. FIG. 2 is a schematic diagram showing the relationship between T, thermal conductivity λ, and bulk density ρ of a heat insulating material. (la) (lb) (lc) = carbon fiber felt, (2a) (2b)...carbide or graphitide, (
3)...graphite sheet

Claims (2)

[Claims] 1. A molded heat insulating material in which multiple layers of carbon fiber felt are bonded with carbide or graphitized material, or bonded with carbide or graphitized material via a graphite sheet, and the bulk density of the carbon fiber felt forming each layer is , a molded heat insulating material characterized in that the bulk density is substantially constant within each layer and gradually decreases in a direction perpendicular to the bonding surface. 2. The molded insulation material according to claim 1, further comprising a graphite sheet on at least one outer surface parallel to the joint surface.